Objects with surfaces having luminous afterglow (phosphorescent) properties are useful as indicators of, for instance, emergency equipment where they can be used to indicate escape routes and location of critical equipment in darkness, such as in the event of a power failure in public buildings or during an emergency situation on a ship or an aircraft. Introduction of phosphorescent properties can also be used for gadgets, toys etc.
Phosphorescent materials are typically solid, crystalline materials and their production usually involves mixing, sintering and grinding to form a powdery material. CN 1053807 and U.S. Pat. No. 5,424,006 teach that efficient phosphorescence can be achieved by the use of e.g. aluminium-strontium oxide doped with europium and dysprosium.
A phosphorescent surface is conventionally produced by forming a paint containing phosphorescent particulate material and applying the paint onto the surface of an object, such as an extruded aluminium profile. A problem with this technique is that the particle size of the phosphorescent material must be kept relatively large to maintain the phosphorescent properties, which means that surfaces treated with such paints become rough with accumulation of dirt and dust particles and a decrease in the luminance capacity over time as a result. Another problem is that the luminous coating is affected by wear and tear and may gradually be worn down. Still another problem is that the painting process can be rather laborious and time-consuming. In addition, only a fraction of the rare earth metal oxides added in the manufacturing process of the long afterglow phosphorescence pigments contribute to the final luminescence of the product, resulting in high production costs.
CA 2005560 discloses a process where an organic luminescent substance is deposited in the pores of an aluminium oxide layer. This process may reduce the problems related to the painting process but the durability of the capacity to store and emit light is uncertain since luminescent organic substances are likely to decompose with time.
Accordingly, there is a need for improvements in the field of providing a phosphorescent surface onto objects for the purpose of, for instance, indicating escape routes and location of critical equipment in darkness.